1. Field of the Invention
The present invention relates to a webbing retractor which structures a seat belt device for restraining, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle or the like.
2. Description of the Related Art
A seat belt device which restrains, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle, is equipped with a webbing retractor which is fixed to the vehicle body at the side of the seat. The webbing retractor has a spool (take-up shaft) whose axial direction runs, for example, substantially along the longitudinal direction of the vehicle. The proximal end side, in the longitudinal direction, of the webbing belt is anchored at the spool. The spool can take up the webbing belt in the form of a roll around the outer peripheral portion of the spool. When the seat belt device is not being used, the webbing belt can be taken-up and accommodated on the outer peripheral portion of the spool.
An urging member, such as a spiral spring or the like which urges the spool in a take-up direction in which the spool takes up the webbing belt, is provided at the webbing retractor. Due to the urging force of this urging member, the webbing belt is taken up and accommodated. In the state in which the webbing belt is applied to the body of a vehicle occupant, slack or the like of the webbing belt is eliminated by the urging force of the urging member.
On the other hand, a mechanism has been conceived of which, when the vehicle rapidly decelerates or the like, takes-up a given amount of the webbing belt onto the spool, so as to eliminate the slight looseness called “slack”, and increase the force by which the webbing belt restrains the body of the vehicle occupant, and even more reliably hold the body of the vehicle occupant. In this type of mechanism, generally, the state of rapid deceleration of the vehicle is detected by an acceleration sensor, and the mechanism forcibly rotates the spool in the take-up direction on the basis of an electric signal from the acceleration sensor.
In contrast, a structure has been thought of in which the distance to another vehicle or an obstacle ahead is detected by a distance sensor or the like. When the distance to the vehicle or the obstacle ahead is less than a given value, a motor is operated, and the spool is rotated in the take-up direction by the torque of the motor.
When the state of rapid deceleration of the vehicle such as that described above is cancelled, this structure, which rotates the spool by the driving force of a motor, can be used to rotate the spool by a predetermined amount in the pull-out direction so as to loosen the webbing belt, thereby lessening the pressing sensation imparted to the vehicle occupant.
However, in a usual state, when the pressing sensation or the releasing sensation is suddenly changed by loosening or tightening the webbing belt suddenly by the driving force of the motor, the vehicle occupant conversely has an uncomfortable sensation. Thus, it is desirable to, at usual times, have the motor drive the spool relatively gently at the time when the motor causes the spool to rotate.